Regional cardiac 31 P-MRSI at 7T: detection of spatially heterogeneous patterns of myocardial energetic impairment
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Background
The phosphocreatine-to-ATP ratio (PCr/ATP), measurable by ³¹P magnetic resonance spectroscopic imaging (³¹P-MRSI), is a sensitive marker of myocardial energetic reserve. Regional energetic-mechanical coupling, evaluable only per-segment to avoid confounding from spatially heterogeneous disease, represents an important target for cardiac metabolic trials. We extend our previously validated 7T regional ³¹P-MRSI approach to patients with cardiovascular disease.
Methods
Twenty-one participants underwent same-day 7T ³¹P-MRSI and 3T CMR: 9 healthy volunteers, 4 with type 2 diabetes, 5 with heart failure, and 3 with ischaemic cardiomyopathy. PCr/ATP was mapped across six mid-ventricular AHA segments. Ejection fraction, global longitudinal strain, peak filling rate, and regional circumferential and radial strain were derived from 3T CMR. Group differences were assessed by Kruskal-Wallis test with Bonferroni-corrected pairwise comparisons; segment-level associations by per-segment Spearman correlation and linear mixed effects models.
Results
PCr/ATP differed significantly across groups (p = 0.005, η² = 0.58), ranging from 1.78 ± 0.21 in healthy volunteers to 1.10 ± 0.28 in heart failure. Mean PCr/ATP correlated with ejection fraction (rs = 0.65, p = 0.002), global longitudinal strain (rs = −0.63, p < 0.001), and peak filling rate (rs = 0.52, p = 0.023). Segment-level energetic-mechanical coupling was significant in the anteroseptal and inferoseptal segments (circumferential strain rs = −0.49 to −0.56; radial strain rs = 0.43 to 0.57, all p < 0.05), with no significant associations in other segments, consistent with a displacement-related measurement quality gradient. In ischaemic patients, PCr/ATP was significantly lower in infarct segments (0.79 ± 0.20) than remote myocardium (1.33 ± 0.22, p = 0.008, r = 0.62). All three ischaemic patients demonstrated remote PCr/ATP below the healthy volunteer median, with two below the 5th percentile (rank-sum p = 0.018; Fisher p = 0.045).
Conclusions
Regional 7T ³¹P-MRSI detects segment-level energetic differences across cardiovascular disease states and reveals spatially specific energetic-mechanical coupling confined to the septal segments in the current ungated acquisition. Energetic impairment in ischaemic cardiomyopathy extends into structurally preserved remote myocardium. These findings support larger studies using regional ³¹P-MRSI to investigate regional energetic-mechanical coupling as a target for metabolic cardiac therapies.
